When you fast, the digestive system gets a break from needing to process, digest, and absorb all the different foods and drinks you normally consume, so jumping right back into your normal diet after a period of prolonged fasting can be an unwelcome shock to your gut.
Additionally, depending on how long you fasted, it may also be helpful to avoid food such as raw cruciferous vegetables, legumes, seeds and seed bladders, and nuts and nut butters.